Techopedia explains Automatic Vehicle Locator (AVL)

Automatic vehicle locator systems provide specific user interfaces for tracking vehicles and finding out more about actual transport in real time. For example, different systems have different features for labeling vehicles, looking at vehicle location history, etc.

In terms of the engineering and design of these systems, they use radio frequency to deliver signals from a vehicle to a central base, which can be as simple as a personal computer attached to the Internet. This is called a "radio to Internet" design, where the base takes the data and sends it over the Internet. Now, companies are designing even newer kinds of systems that can provide extra functionality, such as determining how many passengers are in a given vehicle.